Method and device in radio based telecommunication system using repeaters

ABSTRACT

A radio based communication system including stationary units, portable or mobile units, and repeaters. Respective mobile units communicate using a normal access schedule where transmitting and receiving functions are separated in time, for instance with a half time frame. Reception for a respective current stationary unit is delayed a number of time slots in relation to transmitting from the stationary unit, at which the stationary unit is aware of the delay and consequently the use of a repeater. Also repeating of information is arranged to be performed within one time frame.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method in a radio basedtelecommunication system, preferably the Digital European CordlessTelephone (DECT) system, in which a duplex channel is establishedutilizing repeaters which are performing the repeating without causingserious delays and/or interference.

2. Discussion of the Background

Repeaters in radio based communication systems can for many applicationsbe of very great importance for the economy and functionality of thesystem. One example of a powerful repeater application is the radiobased local network application OMA (Omradesbegransad Mobil Access=AreaRestricted Mobile Access). The application implies that the terminatingwire connection to the subscriber is replaced or completed by a surfacecovering radio. The subscriber is offered terminal mobility within oneor more restricted areas. If repeaters are used the numbers of baseunits can be reduced by a factor of 10-100, resulting in the costs, foramong other things the wire connection of base units, to be dramaticallyreduced. Consequently, repeaters will be very important in futuresystems.

The importance of repeaters has led to DECT-repeaters (Digital EuropeanCordless Telephone) being presently standardized within ETSI (EuropeanTelecommunication Standards Institute) RES-3.

SUMMARY OF THE INVENTION

Compared with previous proposals within the field there is a need forrefining and a need for further development to meet the demands whichhave lately arisen in connection with an ever increasing concentrationon repeaters.

The present invention is based on the knowledge that, for avoidingserious delays, repeating must be performed within one time frame. Thepresent invention solves certain technical problems which occur whenrepeating is performed within one time frame, such as:

How hand over within or between cells is made possible.

How interference between repeaters is avoided in spite of all repeatershaving access to all channels.

How the use of capacity demanding double duplex communication betweenrepeaters and a base station is avoided without the need of separatingrepeating of the control signaling and useful data in different timeframes.

How optimal selection of channels can be performed in spite of theportable not "hearing the base station".

How one, regarding portables, avoids influencing presentDECT-specification.

THE SOLUTION

See the subsequent patent claims.

ADVANTAGES

The present invention achieves system technical advantages by a repeaterfunction. Hand over will be possible between cells and repeaters. Thesystem can be used in a radio system which uses TDMA/TDD/MC. Appropriatefields of application are radio based local networks, systems forwireless Private Automatic Branch Exchanges (PABX), and public access.In connection with the above mentioned applications, the CT-systemDCT900 and DECT may be used in the short run. Notice that it may bequite possible to use one and the same DCT900 or DECT-portable (PP) inall of the above-mentioned applications.

Repeating is made within one time frame. One-way average delay which isadded is therefore <2.5 ms. One does not need to use two duplexconnections between a Radio Fixed Part (RFP) and a Repeater (REP) whichresults in less capacity demanding systems. In addition, CyclicalRedundancy Check (CRC) based macro diversity is possible. Macrodiversity also becomes possible. The present invention implies thatseparation of repeating of control signaling and useful data is notneeded, which simplifies encryption. Repeaters have a large economic andfunctional potential for the above-mentioned systems and for futuresystems using TDMA. The present invention also solves important problemswith repeaters being used in a TDMA-system.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below while, at the same time, isreferred to by the enclosed drawings where:

FIG. 1 shows an example of the radio based network application OMA usingrepeaters,

FIG. 2 shows a method for establishing duplex channels,

FIG. 3 shows a flow chart for repeating in uplink, and

FIG. 4 shows a flow chart for repeating in downlink.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following abbreviations are used:

REP Repeater

PP Portable Part

RFP Radio Fixed Part (corresponding to base station)

ARK Access Rights Key

ARI Access Rights Identity

The following invention gives directives on how repeating withcoding/decoding of control fields can be performed in radio systems withtime shared access, as for instance in DECT. The PP follows a normalaccess schedule, for DECT this implies that transmitting and receivingare separated a half time frame. Reception for the RFP is, on thecontrary, delayed a number of time slots in relation to transmitting forthe RFP.

The RFP, however, must have knowledge of this delay, i.e. that a REP isbeing used.

Example

A. Set up initiated by the RFP

Set up from the RFP is performed by a normal paging message. Selectionof a channel is performed by the PP, whereupon demand for access isreturned by the PP on the selected channel. The REP compares theselection of the channel with a REP channel list. If the channel is notsufficiently silent, there will (see also FIGS. 2 and 3) either be norepetition; instead the PP is informed from the REP that the selectionof channel is not accepted. The message is sent in downlink on thechannel desired by the PP. Or the REP selects another, more silentchannel for the RFP-communication, such one that repetition in downlinkfrom the REP yet can be performed on a channel desired by the PP. Whenaccepted, confirmed channel selection repeating is made in uplink. TheREP adds a message to a control field regarding a present delay, i.e.the channel for RFP>REP-communication. N.B; if such a message islacking, the RFP shall suppose that the delay is zero slots. i.e.communication is performed without the REP, direct with the PP.

B. Set up initiated by the PP

Set up from the PP is performed by access demand on the desired channel.

How to avoid two REPs repeating the same message during uplink?

The PP indicates the desired RFP-identity (corresponding to the FMID,which is geographically unique). But this RFP-id also includes a localREP-unique addition. This addition has been added in downlink by therespective REP.

Possibly the REP can remove the ID-addition in uplink in order not todistract the RFP (see FIG. 3).

How to avoid two REP downlink repeating the same message on the samechannel?

The problem does not exist for established duplex communication becausethe REP knows which duplex channels it is managing. For simplex messagesfrom one and the same RFP, the adjacent RFP should, on the contrary,repeat on different channels to avoid interference. The selection of achannel can be made in such a way that the REP which receives simplextraffic shall repeat on the free latest finished duplex channel by theREP. (Channel change can also be performed by the REP if the PP demands"change dummy bearer position") (see FIG. 4).

How to manage hand over between two REPs (inter REP handover)?

As previously mentioned each REP indicates its local unique identity asan addition to the RFP-identity. This entails that also inter REPhandover is managed--the PP indicates, as we know, indirectly a desiredREP-id at each new access demand.

How to manage hand over between the REP and the RFP?

In the same way as inter REP hand over. The PP "sees" that the REP andthe RFP have different identities. This implies that the REP will notrepeat the new access demand from the PP, because the REP is notaddressed. The RFP occurs a "normal" intra cell hand over, but inaddition with a change of delay between transmission/reception.

Two adjacent REPs can by using a common identity be used for macrodiversity as discussed previously. The REP ought to have an access key(REP-ARK) corresponding to the Park for the PP.

By the REP comparing the REP-ARK with the ARI from the RFP, the REP candecide whether it has the right to repeat from the RFP in question.

The REP-id can also be used by the RFP for addressing a specific REP forsystem updating, trouble shooting, etc. It may for instance be valuableto have an opportunity to change the REP-ARK for a REP. In this way, forinstance, an operator's belonging can be changed.

An emergency call shall be repeated independent of the REP-ARK.

As a further description to FIG. 2, consider an access demand from thePP to the REP on slot (channel) n. The REP selects slots forcommunication with the RFP. For uplink (REP→RFP) the best slot of n+1 toN is selected. For downlink (RFP→REP) the best slot of 1 to n-1-N/2 isselected. At performed channel selection, the REP repeats to the RFP. Ina control field the RFP is informed of a desired channel for thedownlink rep.

The RFP transmits on an approved channel to the REP, which after thatrepeats to the PP on the channel indicated by the PP at theabove-mentioned access demand. After that the now established duplexcommunication proceeds.

I claim:
 1. A method in a radio based telecommunication system, using atleast one stationary unit, at least one portable unit and at least onerepeater in a communication between said units, wherein at anestablishing of a duplex channel between said portable unit and saidstationary unit an access demand is sent from said portable unit to saidrepeater on a time slot n, wherein said repeater selects a best timeslot among time slots n+1 to N for an uplink communication with saidstationary unit, where N represents a number of time slots n in a frametransmitted in said communication between said units, and wherein uplinkcommunication between said portable unit and said stationary unit isestablished and said repeater repeats transmission information to thestationary unit, and that in a downlink communication, a best time slotamong time slots 1 to n-1-N/2 is selected for communication between thestationary unit and the portable unit, wherein said stationary unittransmits on said best slot to said repeater, which repeats transmissioninformation from said stationary unit to the portable unit on said timeslot indicated by the portable unit at said access demand,wherein n+1≦N,and n≧1+N/2.
 2. The method according to claim 1, wherein at anestablishing of a simplex channel a selection is made in such a way thatthe repeater which receives simplex traffic repeats the traffic on thatfree channel which said repeater latest carried a finished duplex. 3.The method according to claim 1, wherein said repeater indicates itslocal unique identity as an addition to an identity of the stationaryunit, which entails that inter repeater handover is managed by means ofthe portable unit indirectly indicating a desired repeater identity ateach new access demand.
 4. The method according to claim 1, whereinhandover between said repeater and said stationary unit is made possiblein that said portable unit knows that the repeater and the stationaryunit have different identities, which implies that said repeater doesnot repeat the new access demand from said portable unit because saidrepeater is not addressed.
 5. The method according to claim 2, whereinthe repeater indicates its local unique identity as an addition to anidentity of the stationary unit, which entails that inter repeaterhandover is managed by means of the portable unit indirectly indicatinga desired repeater identity at each new access demand.
 6. The methodaccording to claim 2, wherein handover between said repeater and saidstationary unit is made possible in that said portable unit knows thatthe repeater and the stationary unit have different identities, whichimplies that said repeater does not repeat the new access demand fromsaid portable unit because said repeater is not addressed.
 7. The methodaccording to claim 1, wherein said uplink and downlink information isformatted to be used in a Digital European Cordless Telephone system. 8.A method of communication in a radio based telecommunication systemincluding at least one stationary unit, at least one portable unit, andat least one repeater, comprising the steps of:transmitting from said atleast one portable unit access demand information to said at least onerepeater on a time slot n; selecting by said at least one repeater abest time slot among time slots n+1 to N for uplink communicationbetween said at least one portable unit and said at least one stationaryunit, where N represents a number of time slots n in a frame transmittedin communication between said at least one stationary unit, said atleast one portable unit, and said at least one repeater; selecting bysaid at least one repeater a best downlink time slot among time slots 1to n-1-N/2 for downlink communication between said at least onestationary unit and said at least one portable unit; repeating by saidat least one repeater the access demand information transmitted fromsaid at least one portable unit to said at least one stationary unit,thereby establishing said uplink communication; transmitting by said atleast one stationary unit downlink information to said at least onerepeater on said best downlink time slot selected by said at least onerepeater; and repeating by said at least one repeater said downlinkinformation transmitted by said at least one stationary unit to said atleast one portable unit, thereby establishing said downlinkcommunication, wherein n+1≦N, and n≧1+N/2.
 9. The method according toclaim 8, wherein the step of repeating said downlink information repeatssaid downlink information on a free downlink time slot which was mostrecently occupied by a previous downlink communication.
 10. The methodaccording to claim 8, wherein the step of repeating said downlinkinformation further comprises the step of:adding data corresponding toan identity of said at least one repeater to said downlink information.11. The method according to claim 8, wherein said access demandinformation transmitted by said at least one portable unit includes datacorresponding to an identity of a desired said at least one stationaryunit.
 12. The method according to claim 8, wherein said at least oneportable unit detects that said at least one repeater and said at leastone stationary unit have different identities.